1. Technical Field
The present invention relates to a heater wherein voltage is applied between opposed electrodes in a pressure-reduced state and an anodic electrode (anode) is heated by electrons emitted from a cathodic electrode (cathode) as an electron source, a fixing device for fixing a toner image with use of the heater, and an image forming apparatus.
2. Related Art
Generally, as a toner image fixing process in an image forming apparatus using a powdered toner, there is widely adopted a process wherein a toner image is transferred electrostatically onto a recording medium, then the recording medium is sandwiched in between a heating member and a pressurizing member to heat the toner image and pressure-bond the toner image to the recording medium.
In such a fixing device, a halogen lamp is in wide use as a heating source for heating the toner image. For example, a fixing roller having a halogen lamp in the interior of a cylindrical core and a pressing roller to be pressed against the fixing roller are provided and a nip portion is formed wherein rotating fixing roller and pressing roller are pressed against each other. A recording medium which carries an unfixed toner image thereon is fed to the nip portion and is conveyed. The fixing roller is heated by radiant heat radiated from the halogen lamp disposed in the interior, whereby the toner image on the recording medium passing through the nip portion is heated and pressurized.
Recently, as a measure against environmental issues it has also been required to suppress the consumption of energy. More particularly, in order to make the aforesaid warming-up time as short as possible and minimize the power consumption in stand-by condition, it is required that a portion of a fixing member for heating a toner image be heated locally efficiently.
In this connection, a fixing device which adopts an electromagnetic induction heating method instead of using a halogen lamp as a heating source is proposed.